Pitch control of an aircraft is the control of the nose-up and nose-down pitch attitude of the aircraft during flight. During changes in pitch attitude, the aircraft pivots about a lateral axis extending through a center of gravity (CG) of the aircraft. Pitch control may be provided by a horizontal tail that may be located aft of the aircraft wings. The horizontal tail may include an adjustable horizontal stabilizer and an elevator. The elevator may be pivotably coupled to the horizontal stabilizer. The angle of incidence of the horizontal stabilizer may be adjusted in a positive and/or negative direction relative to a longitudinal axis of the aircraft to trim the aircraft so that the aircraft is maintained at a constant pitch angle during flight. For example, the horizontal stabilizer may be adjusted at a negative angle of incidence to provide a download so that a nose-up pitching moment is generated about the aircraft CG to counteract a nose-down pitching moment generated by the positive lift of the wings. The load generated by the horizontal tail may be carried by the structure of the horizontal tail and the fuselage.
For nose-up and nose-down pitch maneuvering of the aircraft during flight, the elevator may be pivotably moved upwardly or downwardly from a neutral position relative to the horizontal stabilizer. For example, to maneuver the aircraft from a nose-up attitude to a level attitude, the elevator may be pivotably deflected or positioned downwardly (e.g., elevator trailing edge down) so that the horizontal tail generates an increased amount of upload to bring the nose of the aircraft down. The elevator may be held in the downward position until a level attitude of the aircraft is achieved, after which the elevator may be returned to the neutral position. To maneuver the aircraft from a nose-down attitude to a level attitude, the elevator may be pivotably deflected or positioned upwardly (e.g., elevator trailing edge up) so that the horizontal tail generates an increased amount of download to bring the nose of the aircraft up until a level attitude of the aircraft is achieved.
As the speed of an aircraft increases, dynamic pressure on the horizontal stabilizer and elevator also increases which results in an increase in the upload or download generated by the horizontal tail. To avoid exceeding the load-carrying capability of the horizontal tail and fuselage during nose-up or nose-down maneuvering, the movement or authority of the elevator may be electronically limited as speed increases. Limiting the elevator authority may also provide a more linear or uniform pitch response from pilot input as a function of airspeed. In addition, limiting the elevator authority may prevent excessive maneuvering capability at relatively high dynamic pressure. Unfortunately, excessively limiting the elevator authority as a function of airspeed to reduce tail loads may result in sub-optimal maneuvering capability.
As can be seen, there exists a need in the art for a system and method for moving the elevator within limits that reduce tail loads while providing sufficient authority for pitch control of the aircraft.